From 0af128039e10bd27ac8392d195d3b34f8b1459e7 Mon Sep 17 00:00:00 2001
From: Roland Pallai <dap78@magex.hu>
Date: Fri, 27 Jan 2023 14:29:56 +0100
Subject: [PATCH 081/147] QXcbConnection::getTimestamp: do not return stale
 timestamp

The problem is `PropertyNotify` event generated by
`xcb_delete_property()` at return could be reported as an actual
timestamp at next call due to a missing `state` filter.

Because `PropertyNotify` is generated even if an unchanged property
value is set we can get rid of this delete event easily.

This issue causes observable problems in kwin_x11 (KDE project)
too.

Fixes: QTBUG-56595
Pick-to: 5.15 6.2 6.4 6.5
Change-Id: Ice6cfa934e3769d86e9f7264e369dc5918c8542a
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: JiDe Zhang <zhangjide@uniontech.com>
(cherry picked from commit 03ac8c7397b9f070a8ef5f33b4675411293b0723)
---
 src/plugins/platforms/xcb/qxcbatom.cpp       | 2 ++
 src/plugins/platforms/xcb/qxcbatom.h         | 2 ++
 src/plugins/platforms/xcb/qxcbconnection.cpp | 6 ++----
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/plugins/platforms/xcb/qxcbatom.cpp b/src/plugins/platforms/xcb/qxcbatom.cpp
index 780816605a..a769ddadbd 100644
--- a/src/plugins/platforms/xcb/qxcbatom.cpp
+++ b/src/plugins/platforms/xcb/qxcbatom.cpp
@@ -90,6 +90,8 @@ static const char *xcb_atomnames = {
 
     "_QT_CLOSE_CONNECTION\0"
 
+    "_QT_GET_TIMESTAMP\0"
+
     "_MOTIF_WM_HINTS\0"
 
     "DTWM_IS_RUNNING\0"
diff --git a/src/plugins/platforms/xcb/qxcbatom.h b/src/plugins/platforms/xcb/qxcbatom.h
index 9cf93ec314..1ce6cca573 100644
--- a/src/plugins/platforms/xcb/qxcbatom.h
+++ b/src/plugins/platforms/xcb/qxcbatom.h
@@ -91,6 +91,8 @@ public:
         // Qt/XCB specific
         _QT_CLOSE_CONNECTION,
 
+        _QT_GET_TIMESTAMP,
+
         _MOTIF_WM_HINTS,
 
         DTWM_IS_RUNNING,
diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index 533018f35b..631ade2ec7 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -804,8 +804,8 @@ xcb_timestamp_t QXcbConnection::getTimestamp()
 {
     // send a dummy event to myself to get the timestamp from X server.
     xcb_window_t window = rootWindow();
-    xcb_atom_t dummyAtom = atom(QXcbAtom::CLIP_TEMPORARY);
-    xcb_change_property(xcb_connection(), XCB_PROP_MODE_APPEND, window, dummyAtom,
+    xcb_atom_t dummyAtom = atom(QXcbAtom::_QT_GET_TIMESTAMP);
+    xcb_change_property(xcb_connection(), XCB_PROP_MODE_REPLACE, window, dummyAtom,
                         XCB_ATOM_INTEGER, 32, 0, nullptr);
 
     connection()->flush();
@@ -837,8 +837,6 @@ xcb_timestamp_t QXcbConnection::getTimestamp()
     xcb_timestamp_t timestamp = pn->time;
     free(event);
 
-    xcb_delete_property(xcb_connection(), window, dummyAtom);
-
     return timestamp;
 }
 
-- 
2.40.1